1. Field of the Invention
The invention relates in general to the firing of ceramic greenware and more particularly to apparatus for supporting ceramic insulator greenware to prevent distortion of same during the firing process.
2. Description of the Prior Art
Ceramic greenware is subject to shrinkage during the firing process. Because of this, the surface upon which the ceramic greenware resides, i.e., the load bearing surface, is subject to distortion due to friction between the load bearing surface and the support surface upon which the greenware resides. This distortion due to shrinkage or contraction of the greenware during the firing process becomes critical for ceramic insulator greenware in particular, because the ceramic insulator greenware is supported during the firing process on a portion of the insulator that later is used for insertion into the mounting flange ring of a transformer or other electrical apparatus where ceramic insulator bushings are employed. A small amount of distortion then of a ceramic insulator load bearing surface causes the fired insulator to be unsuitable for mounting in the end use electrical apparatus. A known solution of the prior art to alleviate this distortion problem is the use of an unfired setter plate disposed between a fired setter plate and the load bearing surface of the ceramic greenware. The unfired setter plate then contracts uniformly with the ceramic greenware since both are greenware. The load bearing surface of the ceramic greenware is not required to slide over the support surface and no distortion occurs. The disadvantages of this method are the increased labor necessary to level the setter plates prior to firing of the ceramic greenware and the increased material cost because it is necessary to scrap the green setter plate after it has been fired. Only green setter plates are suitable for uniform contraction with the load bearing surface of the ceramic greenware. The increased labor to level the green setter plate as well as the waste materials resulting from throwing away the green setter plate after firing add to the cost of the final fired ceramic insulator product. Accordingly, it would be desirable to provide a reusable greenware support that would provide a level support surface for the load bearing surface of the greenware that would allow shrinkage of the greenware load bearing surface during firing so as to prevent distortion.